In order to protect electronic components, which in today's technology are arranged on a side of printed circuit boards with preapplied conductor strips, for example from corrosion, it is known to coat these components and the parts of the printed circuit boards carrying these components with an insulating lacquer, which also protects the conductor strips printed on the circuit board against short-circuits which can be caused by dirt.
Such films can be manufactured using the so-called dipping process. However, surface areas which are not to be coated, for example surface areas which must have exposed conductors in order to enable contact with further printed circuit boards or supply connections, must then be covered through expensive gluing operations. This process is time-consuming and therefore expensive. The same is true when the printed circuit boards are coated by applying the insulating lacquer with a brush, which may yet be economical when the printed circuit boards are very small and/or when only small areas or areas with a very complicated design must be coated, namely in special cases and only in small quantities.
For the above purpose it is also known to utilize coordinate-controlled coating devices, which apply the coating linearly, either by pouring or by spraying. However, such devices are not only expensive, but also operate relatively slowly because of the linear application of the coating, with the result that their use, regardless of the achievable automation of the coating process, is also expensive.
A summary of possible coating processes is disclosed in the publication by Peter A. Knoedel "The protective lacquering of occupied printed circuit boards", Metalloberflaeche, 1989/4+5.
A process known from U.S. Pat. No. 4,794,018 is also part of these known processes, in which process the printed circuit boards which are to be coated are engaged by a stream of liquid coating material guided through a flat vat. The stream is created by a pump, which moves the coating material from a storage container into the vat, from which the coating material can flow off into a lower lying collecting vessel. Depending on the depth of immersion of the printed circuit boards, both their underside and also their upper side can thereby be coated. Edge areas which are not supposed to be coated are arranged outside of wall recesses of the vat, through which recesses the coating material can flow off into the collecting vessel. It is practically impossible with this process to exclude inner areas of the boards, which are enclosed by areas to be coated, from the coating.
Further coating processes, by means of which precisely limited areas of bodies can be coated, are known from German Offenlegungsschrift No. 28 48 569 and from U.S. Pat. No. 3,853,663.
The process according to German Offenlegungsschrift 28 48 569 is used for coating ceramic or porcelain articles like cans, vases or the like with a glazing material, in which all surface areas must be glazed with the exception of a circular, narrow, lower outer edge of the bottom which, in its center area, is slightly concavely inwardly arched. The container is placed onto a flexible plate, which covers the inside of a storage container for the glazing material, but which has one opening through which the inside of the container communicates with the flatly concavely arched space defined by the arched bottom, which space is bounded by the base. The article is pressed against the flexible plate by a vacuum induced inside of the storage container not filled with the glazing material. By pivoting the storage container and the article held on the storage container, the bottom area within the base is glazed. By dipping the article with the storage container still attached into a further storage container, which is filled with glazing material, the remaining surface of the article is glazed, which surface is formed by its outer and inner wall surfaces and the inside of its bottom.
The process known from U.S. Pat. No. 3,853,663 is used to coat circular surfaces of tennis ball halves which have the shape of half shells of a ball with a liquid adhesive, and which after their annular surfaces are coated are pressed on one another in order to achieve a material-flow fixedly connected ball shell core- The ball halves to be coated are thereby arranged above the liquid level of the adhesive provided in a container so that the annular surface used for gluing is spaced a small distance from this level. A ring is arranged in the container below the liquid level, the average diameter of the ring corresponding with the average diameter of the surface to be coated. By lifting this ring, an annular wave of coating material is, so to speak, produced between the ring and the annular surface to be coated, which wave reaches the annular surface of the ball half and moistens same. This process has the purpose of assuring that only the annular edge of the ball halves is coated, and not the outer areas of the ball halves, which would make their further treatment more difficult. At best, "linear" areas of bodies to be connected with one another can be coated with this process, but not flat areas which have relatively large cross-sectional surfaces.
In view of the above-mentioned disadvantages of known coating processes, a purpose of the invention is first to provide a process of the above-mentioned type which enables an efficient and reliable coating of complicated coating surfaces on printed circuit boards, and a device for carrying out the process.